The document discusses carbohydrates, which are sugars and their derivatives that provide energy. Carbohydrates are classified as monosaccharides (simple sugars like glucose), disaccharides (two monosaccharides bonded together like sucrose), or polysaccharides (long chains of monosaccharides like starch). Glucose is the most common and important monosaccharide for living organisms. Carbohydrates can exist as open-chain or cyclic ring structures and have D and L stereoisomers depending on the orientation of hydroxyl groups. Important carbohydrates include glucose, fructose, and ribose which make up disaccharides and nucleic acids.

1. Notes Carbohydrates
Introduction:
The three main classes of molecules metabolized by our bodies:
1. Carbohydrates (sugars)
2. Lipids (fats)
3. Proteins (amino acids)
Carbohydrates are defined as sugars and their derivatives. Animals (such as humans) break
down carbohydrates during the process of metabolism to release energy. For example, the
chemical metabolism of the sugar glucose is shown below:
glucose + oxygen → carbon dioxide + water + energy
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy
Animals obtain carbohydrates by eating foods that contain them, for example potatoes, rice,
breads, etc. These carbohydrates are manufactured by plants during the process of
photosynthesis. Plants harvest energy from sunlight to run the reaction described above in
reverse:
6 CO2 + 6 H2O + energy (from sunlight) → C6H12O6 + 6 O2
A potato, for example, is primarily a chemical storage system containing glucose molecules
manufactured during photosynthesis. In a potato, however, those glucose molecules are bound
together in a long chain. As it turns out, there are two types of carbohydrates, the simple sugars
and those carbohydrates that are made of long chains of sugars - the complex carbohydrates.
The simplest carbohydrates are the monosaccharide, a single unit simple sugar.
The most common monosaccharide is glucose, and this is the most important one for living
organisms.

4. Metabolism:
Processes require energy. The term metabolism is associated with energy. This is just one
aspect of metabolism.
Metabolism more specifically refers to a sequence of chemical reactions used to produce one or
more products or accomplished one or more processes.
Returning to energy, per gram fats provide the most energy, carbohydrates provide the next
most and proteins provide the least energy. The energy of carbohydrates is the most quickly
utilized. Think about a 4 year old after sneaking into their Halloween candy bag. They are full
of energy!
Structure of Carbohydrates:

5. Lets break down the word carbohydrate. Carbo = carbon and hydrate = water leading one to
believe carbohydrates are hydrates of carbon. Remember a hydrate is a compound which has
water loosely attached. An example would be FeCl3 • 6 H2O. This is iron(III) chloride
hexahydrate. Each FeCl3 salt molecule has absorbed 6 water molecules. These are not
chemically bound and can be removed by heating leaving FeCl3 and H2O. Since the chemical
formulas are unchanged there has been no chemical reaction, it has undergone a physical
process.
C O
H
C
C
H OH
C
H OH
C
H OH
H
H OH
Ribose
From the above carbohydrate ribose, it should be easy to see why the products of heating
carbohydrates is water and a black soot, carbon. When heated the OH groups combine with
their associated H and form water, leaving elemental carbon, a black soot. But these are clearly
chemical bonds and not hydrates of water. By the way, the R in RNA is ribose.
If you look at the structure of the saccharides you will find they are either an aldehyde or a
ketone. Carbohydrates are either polyhydroxy aldehydes or polyhydroxy ketones. Remember,
poly means many, hydroxy refers to –OH groups and that the carbonyl carbon is either the
terminal carbon, therefore an aldehyde, or it is not a terminal carbon, therefore a ketone. The
aldehyde saccharides are called aldose and the ketone saccharides are called ketose.
The ribose above is an aldehyde. The carbonyl is the terminal carbon.
examples:
C O
H
C
C
H OH
H OH
H
glycer aldehyde
2,3-dihydroxypropanal 1,3-dihydroxy-2-propanone
dihydroxy acetone
C
H
C
C
O
H OH
H
OHH
The structure of saccharides shows them to contain stereocenters. Even the most simple
saccharides, glyceraldehydes have a stereocenters on its central carbon. The following section
is a review of stereo chemistry.

6. Isomers: Stereoisomers
The stereoisomer is a special type geometric isomer. The connectivity is the same between two
stereoisomers, the difference is their arrangement in 3-dimensional space. They are mirror
images of each other. They are not super imposable. Your hands are mirror images of each
other, they are the same, but opposites. Another term used is chiral, this would be used to
describe a carbon that is a stereocenter, the chiral carbon, or a molecule with a stereocenter is
a chiral molecule.
This phenomenon only occurs around carbon atoms that have 4 different connections. The
example below shows 4 different atoms, but chains of atoms, for instance a methyl group, could
be substituted for these individual atoms. See the second image down.
Example:
One of the following three carbons is chiral, which is it and why are the other two not chiral?
Example A is the chiral carbon. Both B and C do not have 4 different connections. Example B
has 2 hydrogen atoms attached to the carbon and example C has 2 methyl groups attached to
the carbon.
When this occurs the two mirror images are called enantiomers. The two molecules will have
the same name except for a prefix(s). These prefixes originate in one of the properties of
compounds with stereocenters, rotation of plane polarized light or in the convention of drawing
the structures.
This may not seem like an important point, but as it turns out, even though these two molecules’
structures are almost exactly the same, they do react differently. Sometimes with terrible
consequences.

7. C O
H
C
C
H OH
C
H OH
C
H OH
H
H OH
Ribose
To determine the number of isomers a compound will form:
1. Count the number of stereocenters in the molecule
2. Take 2 to that power
• The ribose molecule to the right has 3 stereocenters.
• 23
= 8
• Ribose will have 8 different isomers.
Carbohydrate Polymer:
Carbohydrates are also referred to as saccharides. Saccharides can be found in several forms.
single monosaccharide
pair disaccharide
many polysaccharide
monosaccharide
• basic unit of metabolism
• normally 3, 4, 5, 6 or 7 carbons in length
• classified as aldose or ketose
• classified as D or L isomers based on the stereochemistry
disaccharide
• use to transport monosaccharides
• water soluble – as they are short hydrocarbon chains
• are sweet to taste
• sucrose, galactose and lactose
polysaccharides
• structure of plants – cellulose
• storage of monosaccharides

8. The D and L prefixes are generated by the convention of drawing the structures. If the -OH
group on the carbon before the terminal carbon is on the left it is designated with an L; if the
-OH group on the carbon before the terminal carbon is on the right it is designated with an D.
You may ask why the -OH group on the carbon before the terminal carbon, why not use the
terminal carbon? Well the terminal carbon will not be a stereo center, there will normally be 2
hydrogens on that terminal carbon.
So, if you draw these monosaccharides vertical with the carbonyl carbon on the top or as close
to the top as possible it will make identifying them easier.
C O
H
C
C
H OH
H OH
H
D-glycer aldehyde
D-2,3-dihydroxypropanal L-2,3-dihydroxypropanal
L-glycer aldehyde
C O
H
C
C
HO H
H OH
H
These structures are normally drawn in a more simplified manner, because as we know
chemists are lazy. Below you will find a drawing of a Fischer projection along side its equivalent
structures. The Fischer projection is named after Emil Hermann Fischer, winner of the 1902
Nobel Prize in Chemistry.
CHO
CH2OH
OHH
OHH
HHO
OHC
HOH2C OH
H
H
OH
OH
H
C O
H
C
C
H OH
H OH
C
C
HO H
H
H OH
This structure is an L enantiomer. The –OH on the carbon before the terminal carbon is on the
left.
What is the name of this structure? We already have the first piece, L. The carbon chain is 5
carbons long, therefore it is a pent. Lastly, the carbonyl carbon is an aldehyde.
L-aldopentose

9. Draw the Fischer Projections for lactic acid given the following structure:
CH3CHCOOH
OH
COOH
CH3
OHH
COOH
CH3
HHO
D L
Example:

10. Importance of Carbohydrates:
• Very effective energy yield
o contains carbon
o has a reactive bond – carbonyl carbon and is a polar area
o does not have 4 bonds to oxygen – which means the carbon is organic carbon,
remember that organic carbon is carbon with an low oxidation number, once the
oxidation number becomes + 4 it can no longer be oxidized
• Effective building material
o strong not brittle – will bend and not break
• H2O soluble
o easily transported thru the blood stream
o easily passes thru cell walls
• Sugars are carbohydrates.
• Sucrose was used as the standard, all other sugars sweetness is based on sucrose.
carbohydrat
e
relative
sweetness
class
common
name
sucrose 1.00 disaccharide table sugar
lactose 0.16 disaccharide milk sugar
maltose 0.32 disaccharide malt sugar
glucose 0.74
monosaccharid
e
blood sugar
galactose 0.22
monosaccharid
e
-
fructose 1.74
monosaccharid
e
fruit sugar
Saccharide Monomers: (important)
Glucose
• classified as an aldohexose – as it is an aldehyde and a 6-carbon compound
• Most carbohydrates are converted to glucose to be metabolized for energy.
• dextrose and blood sugar are both common names for glucose
• one of the monomers found in the disaccharide found in sucrose, maltose and lactose
• a monomer of starch, cellulose and glycogen
• 25% less sweet than table sugar, sucrose
• no digestion needed can be given intravenously
• found in the urine of diabetics
• 70-150mg per dl of blood

11. C
H
O
OHH
HHO
H OH
H OH
CH2OH
C
H
O
OHH
HHO
H OH
HO H
CH2OH
L-glucose D-glucose
Galactose
• classified as an aldohexose – as it is an aldehyde and a 6-carbon compound
• found in pectin and gum
• combined with glucose to form the disaccharide lactose
• 80% less sweet than table sugar, sucrose
• Galactosemia
o genetic disease – inability of body to metabolize galactose
o elevated levels of galactose in blood and urine
o vomiting, diarrhea, liver enlargement
o can cause death in days
o lactose must be removed from their diet
o http://www.galactosemia.org/galactosemia.htm
• isomer of glucose the #5 carbon has the hydroxyl and hydrogen switched

12. carbon #5carbon #5
D-galactoseL-galactose
C
H
O
OHH
HHO
HO H
HO H
CH2OH
C
H
O
OHH
HHO
HO H
H OH
CH2OH
Fructose
• classified as a ketohexose as this molecule is a ketone and is a 6-carbon chain
• found in fruit juice and honey
• combined with glucose to form the disaccharide sucrose
• 175% sweeter than table sugar, sucrose
• this country’s most common sweetener
o high fructose corn syrup
o can be metabolized to glucose in the liver
CH2OH
C O
HHO
H OH
H OH
CH2OH
D-fructoseL-fructose
CH2OH
C O
HHO
H OH
HO H
CH2OH
Cyclic Saccharides:
The straight form of saccharides is very reactive. For the saccharide to be stable enough to
transport, it forms a cyclic structure. Below are drawings for the formation of straight-chained
glucose to become cyclic. The reaction breaks the double bond of the carbonyl group and shifts
hydrogen of the hydroxyl group on the number 5 carbon to the carbonyl group’s oxygen.

13. D-glucose
C
H
O
OHH
HHO
H OH
H O
CH OH
H
H
carbon 5
C C
C
OC
C
CH2OH
H
H
OH
HO
HOH
H
HO
H
O
CH2OH
H
H
OH
HO
HOH
H
HO
Hcarbon 1
carbon 2
carbon 3
carbon 6
carbon 5
carbon 4
Glucose is classified as an aldose, this ring structure will also form with the ketose saccharides
like fructose.
CH2OH
C O
HHO
H OH
H O
CH2OH
H
D-fructose
O
HO
OH
HOH2C
H
H
H
CH2OH
OH
The stereochemistry of these molecules can become overwhelming. As such other prefixes
must be introduced to describe the stereochemistry, alpha, α and beta, β. Below is the cyclic
structure of glucose. The carbon to the far right on each ring shows the hydroxyl group in
different location. The alpha structure has the hydroxyl group down and the beta group has the
hydroxyl group up.
α-D-fructose

14. O
CH2OH
H
H
OH
HO
HOH
H
HO
H
O
CH2OH
H
HO
HOH
H
HO
H
OH
H
Rings of different numbers of sides are given different names. A five-sided ring is called a
furanose and a six-sided ring is called a puranose.
These are the straight and cyclic structures for fructose, a five carbon ketose.
O
HO
OH
HOH2C
H
H
H
OH
CH2OH
CH2OH
C O
OHH
H OH
H OH
CH2OH
carbon 1
carbon 2
carbon 3carbon 4
carbon 5
carbon 6
Below are the two furanose rings of fructose. The alpha is on the left, hydroxyl on the down.
The beta on the right, hydroxyl on the top.
O
HO
OH
HOH2C
H
H
H
OH
CH2OH
O
HO
OH
HOH2C
H
H
H
CH2OH
OH
These are the straight and cyclic structures for ribose, a six carbon aldose.
β-D-glucose α-D-glucose
α-D-fructose β-D-fructose
D-fructose
D-fructose

15. O
H
OH
HOH2C
H
H
OH
OH
H
H
C O
OHH
H OH
H OH
CH2OH
Below are the two furanose rings of ribose. The alpha is on the left, hydroxyl on the down. The
beta on the right, hydroxyl on the top.
O
H
OH
HOH2C
H
H
OH
OH
H
O
H
OH
HOH2C
H
H
OH
H
OH
As stated in the beginning of these notes, the R in RNA is from ribonucleic acid. The D in DNA
is a molecule whose structure is very close to that of ribose; the molecule is deoxyribonucleic
acid. Lets break down that word. The prefix “de“ means loss, “oxy” means oxygen and “ribo”
refers to ribose. So, what you have is a ribose that has lost an oxygen.
O
H
OH
HOH2C
H
H
H
OH
H
O
H
OH
HOH2C
H
H
OH
OH
H
ribose deoxyribose
This may not seem like much of a change, but this demonstrates the specificity of chemistry.
One oxygen can change the function of a molecule from making proteins, RNA, and storing the
organism genetic information, DNA. Both of the above molecules are furanose, 5-member rings
and are in the beta form, the hydroxyl is up.
Disaccharides:
• The three most important disaccharides are sucrose, lactose and maltose.
• The monomers are very specific. Meaning you must have stereochemistry exact, the bond
will require an alpha or beta and always the D form.
• Disaccharides are formed thru a dehydration reaction.
• This reaction releases a water molecule.
• To break this bond, named a glycosidic bond, you add water, this reaction is named
hydrolysis.
• Where in your body will this digestion occur?
α-D-ribose β-D-ribose

17. Sucrose:
• most common disaccharide, table sugar
• 20% of sugar cane is sucrose
• based on the total consumption in this country, it is estimated that a person will consume 100
pounds of sucrose each year
• it is composed of one α-D-glucose and one β-D-fructose monomer
• not a reducing sugar therefore no reaction occurs with the Benedict’s reagent
• this reaction will not occur because there is no way to open ring and form an aldehyde
• in an acidic solution sucrose undergoes hydrolysis, the resulting solution containing glucose
and fructose is sweeter than the original sucrose
• this can be observed in jams and jellies, the acid in the fruit’s juice, normally citric acid,
causes the sucrose to undergo hydrolysis
• linked α-1 → β-2
• this linkage information tells you that the α-D-glucose molecule uses its #1 carbon, whose
OH group is down, to bond to the #2 carbon on the β-D-fructose molecule, whose OH group
is up
• the reaction and structures are drawn below
O
CH2OH
H
H
OH
HO
HOH
H
HO
H
4 1
H2O
O
HO
OH
HOH2C
H
H
H
OH
CH2OH
1
2
2
1
O
HO
OH
HOH2C
H
H
H
CH2OH
14
O
CH2OH
H
H
HO
HOH
H
HO
H
O
sucrose
α-D-glucose
β-D-fructose

18. Lactose:
• milk sugar
• by mass composes 7% of human milk, 5% of bovine milk
• being lactose intolerant is a fairly common condition, especially in adults who drink less milk,
the body forgets how to make the enzyme, lactase, needed to break lactose’s glycosidic
bond
• it is composed of one α-D-glucose or β-D-glucose and one β-D-galactose monomer
• Lactose is odd in the fact that the second monomer can have either α or β stereochemistry
• is a reducing sugar therefore when tested with Benedict’s reagent the solution turns from a
clear light blue color to a cloudy rust/brown color
• this reaction will occur because when the ring opens an aldehyde can form
• in an acidic solution lactose undergoes hydrolysis, the resulting solution containing glucose
and galactose
• linked β-1→ 4
• this linkage information tells you that the α-D-glucose molecule uses its #4 carbon to bond to
the #1 carbon on the β-D-galactose molecule, both of which have a OH group in the up
position
• the dehydration of one α-D-glucose and one β-D-galactose monomer to form water and
lactose
O
CH2OH
H
HO
HOH
H
H
HO
OH
H
O
CH2OH
H
H
OH
HO
HOH
H
HO
H
1
4 1
4
H2O 4
14
1
O
CH2OH
H
H
OH
HO
HOH
H
H
O
CH2OH
H
HO
HOH
H
H
HO
H
O
α-D-glucose
β-D-galactose
lactose

19. Maltose:
• malt sugar
• it is composed of α-D-glucose monomers
• is a reducing sugar therefore when tested with Benedict’s reagent the solution turns from a
clear light blue color to a cloudy rust/brown color
• this reaction will occur because when the ring opens an aldehyde can form
• in an acidic solution maltose undergoes hydrolysis, the resulting solution containing glucose
• linked α-1→ 4
• this linkage information tells you that one α-D-glucose molecule uses its #1 carbon to bond
to the #4 carbon on the other α-D-glucose molecule, both of which have a OH group in the
down position
14
O
CH2OH
H
H
OH
HO
HOH
H
HO
H
O
CH2OH
H
H
OH
HO
HOH
H
HO
H
4 1
O
CH2OH
H
H
HO
HOH
H
HO
H
O
4 1
O
CH2OH
H
H
OH
HO
HOH
H
H
4 1
H2O
maltose
α-D-glucoseα-D-glucose

20. Polysaccharides:
Starch:
There are 2 classes of starch, animal and plant. Glycogen in animal starch; amylose and
amylopectin are plant starch.
Plant starch is the major storage carbohydrate (polysaccharide) in higher plants, being the end
product of photosynthesis. Starch is composed of a mixture of two polymers, an essentially
linear polysaccharide -amylose, and a highly branched polysaccharide - amylopectin. Starch is
unique among carbohydrates because it occurs naturally as discrete granules (or grains). Starch
granules are relatively dense, insoluble and hydrate only slightly in cold water.
Amylose - The constituent of starch in which anhydroglucose units are linked by α-D-1→ 4
glucosidic bonds to form linear chains. The level of amylose and its molecular weight vary
between different starch types. Amylose molecules are typically made from 200-2000
anhydroglucose units. Aqueous solutions of amylose are very unstable due to intermolecular
attraction and association of neighboring amylose molecules. This leads to viscosity increase,
retrogradation and, under specific conditions, precipitation of amylose particles. Amylose forms
a helical complex with iodine giving a characteristic blue color. This is what you think of when
you think of starch, the meat of a potatoes.

21. Animal Starch, glycogen, is a polymer of glucose. This is stored in the liver and for quick
energy. Glycogen can be quickly hydrolyzed to form glucose and deposited into the blood
stream for transport to cells. Glycogen is highly branched. The chain glycosidic linkage is α-1→
4, the branching occurs with a glycosidic linkage of α-1→ 6.

22. Cellulose:
Cellulose is yet a third polymer of the monosaccharide glucose. The below diagram is of a
portion of a cellulose chain. The glucose monomers are connected by a β-1→ 4 linkage, this
prevents most organisms, including humans from breaking the glucose monomers apart.
Cellulose gives plants their structure, in their cell walls, for example wood fiber. It is also
insoluble.
Cellulose differs from starch and glycogen because the glucose units form a two-dimensional
structure, with hydrogen bonds holding together nearby polymers, thus giving the molecule
added stability (shown in the smaller diagram in the upper right hand corner of the diagram
below.
Cellulose, also known as plant fiber, cannot be digested by human beings and so cellulose
passes through the digestive tract without being absorbed into the body.
Some animals, such as cows and termites, contain bacteria in their digestive tract that help
them to digest cellulose.
Cellulose is a relatively stiff material, and in plants cellulose is used as a structural molecule to
add support to the leaves, stem and other plant parts.
Despite the fact that it cannot be used as an energy source in most animals, cellulose fiber is
essential in the diet because it helps exercise the digestive track and keep it clean and healthy.

23. Starch vs. Cellulose:
Starch is a form of so-called polysaccharides - macromolecules composed of thousands of
small sugar molecules. Starch consists of glucose molecules - and so does cellulose. Starch is
used by plants to store energy and is digested when the need for energy arises, e.g., when a
seed germinates. Starch may also be digested by humans and most animals. In contrast,
cellulose is a structural polysaccharide. It forms cellular walls in plants and is thus present in all
plant tissues. In may be found concentrated in wood and straw. Cellulose cannot be digested by
humans and most animals but has an important function as dietary fiber in our diet. In
ruminants, cellulose is broken down in the rumen by resident microorganisms into smaller
fragments which are subsequently utilized by the microorganisms and the ruminant. Decayed
microorganisms are also digested and utilized by the ruminant.
There are differences in the molecular structure between the two polysaccharides: Starch
consists of alpha-D-glucose and cellulose consists of beta-D-glucose. In the diagram, a starch
segment of 3 glucose units (S) is shown at the top and a 3-glucose unit segment of cellulose (C)
is shown below it. The first oxygen atom in each segment is below the plane of the sugar ring
and the hydrogen atom on the first carbon atom is above that plane. Thus, all — CH2OH groups
are above the plane in the starch molecule but their positions alternate in cellulose.

24. Reactions of Carbohydrates:
The enzymes that break down polysaccharides are specific to the type of linkage in the
polysaccharide. The enzyme, cellulase, that hydrolyze the beta linkages in cellulose are
different from the enzyme, amylase, that hydrolyze alpha linkages. The beta linkages are not
broken down by the enzymes that people have and consequently, cellulose does not provide
glucose in our diets. This is the case because most organisms simply do not have the cellulase
enzyme in their bodies, but they do have the amylase enzyme.
Benedict’s test, used with disaccharides to distinguish between sucrose, maltose and lactose.
Lactose and maltose react to change the Benedict Reagent from a clear blue solution to a
cloudy rust/brown solution, but sucrose does not react.
Iodine test, used to check for the presents of starch, specifically amylose. An amylose
compound will turn the iodine solution black.
Fermentation will occur when an enzyme found in yeast reacts with sucrose or maltose to
create ethanol and carbon dioxide gas. No fermentation will occur with lactose. Yeast does not
have that enzyme.
Artificial Sweeteners:
These sweeteners are normally used to reduce a person’s the caloric intake. They work two
ways. First, your body will not be able to metabolize the molecule, even though it can taste it.
So it passes right thru you. Second, the artificial sweeteners are much sweeter, so you need
much less than you would for conventional sugars.
For example Sucralose, the newest artificial sweetener is approximately 6000 times sweeter
than sucrose. Meaning you would need 6000 times less Sucralose than sucrose.
Sucralose taste a lot like sucrose, because it is made from sucrose. Below is the structure of
each.
sucrose
O
CH2OH
H
H
HO
HOH
H
HO
H
O
O
HO
OH
HOH2C
H
H
H
CH2OH
O
HO
OH
H
H
H
CH2Cl
CH2Cl
O
CH2OH
H
H
HO
HOH
H
H
O
Cl
Sucralose